a.

1. 警觉的；警惕的；留神的[（+to）]
   She is alert to every sound and movement.

   她对每一个声音和动作都很警觉。

2. 机敏的，灵活的[（+in）]
   The boy was alert in answering the stranger's questions.

   男孩很机敏地回答了陌生人的问题。

n.[C]

1. 警戒，警报
2. 警戒状态；警戒期间
   She was always on the alert for some new calamities.

   她总是保持警觉以防某种新的灾难。

vt.

1. 向……报警；使警觉；使注意[（+to）]
   The doctor alerted me to the danger of a heart attack.

   医生提醒我注意心脏病发作的危险。

2. 通知（军队，船只等）待命；通知[（+for/about）][O2]
   She's alerted me for weekend duty.

   她已通知我周末值班。

adj.

n.

1. the state of being alert:
   everyone should be on the alert for terrorists.
2. a warning of danger.
3. a prompt or similar signal on an electronic device.

v.